Published by Utah State University Extension and Utah Plant Pest Diagnostic Laboratory ENT-149-11 September 2011 Eriophyid bud, blister, gall, and rust mites

Ryan S. Davis, Diagnostician and Taun Beddes, Cache County Horticulture Agent

What you should know

• Eriophyid mites cannot be seen without a 20x hand lens or greater magnification. • Eriophyid mites seldom cause serious injury or stress to plants; damage is normally aesthetic. • Damage from eriophyid mites usually consists of leaf galls, bud or flower galls, blisters, scabbing, and deformities of leaves, stems, buds, and flowers. • Control techniques include pruning, plant removal, insecticidal soap, horticultural oils, predatory mites, and broad-spectrum insecticides and miticides.

Fig. 2. Microscopic view of an eriophyid (Aceria Introduction anthocoptes).2 Eriophyid mites are translucent, cigar-shaped microscopic mites that cause deformities on many plants species. described from around the world with many species still These mites are noticed when their feeding causes abnor- undescribed. Needless to say, you are likely to encounter malities of plant tissues such as erineum, galls, brooms, these mites some time in your gardening future. leaf curling, blisters, rusts, silvering, fruit rusetting, and de- formed buds, catkins, fruits, etc. Fortunately, these mites rarely cause serious harm to plants, and control is seldom needed. In fact, eriophyid mites can serve as an alterna- General biology tive food source for predatory mites when their primary Family Name: food source is absent. In that way, eriophyid mites can actually help reduce outbreaks of spider mites and other Range: Worldwide insects on which predatory spider mites feed, by allow- Hosts: Some mites are host specific, while others attack ing predatory mites to survive in the absence of their many plant, tree, and shrub species (Table 2). primary food. There are 1,859 species of eriophyid mites Identification of Adult:Nearly invisible to the unaided eye (1/100” in length), cylindrical/cigar-shaped, tapering from head to rear, and translucent white (Fig. 1). Unlike most mites, eriophyids only have 4 legs located near the head. Life History: Mites generally overwinter as fertilized adult females under bud scales, or protected sites on or near the host plant, and emerge at bud break in spring. Both males and females are present throughout the growing season. Reproduction is continuous, with generations completed every 2-3 weeks; overlapping generations are present. Key Habits: Overwintering females emerge from under budscales and other protected sites to lay eggs and feed on new foliage when buds begin to break in the spring. This time is most adventitious for insecticide applications. Fig. 1. Citrus rust mite (Phyllocoptruta oleivora).1 Some may transmit viruses that can deform plants or General biology contINUED cause economic losses to various crops.

Damage description: Below are pictures of symptoms caused by eriophyid mites categorized by plant part.

Fig. 9. Cottonwood catkin gall mite ( newesse- Fig. 10. Ash flower gall mite (Eriophyes fraxiniflora).1 gi).3

Fig. 3. Galls caused by boxelder pouchgall mite (Eriophy- Fig. 4. Leaf blisters on pear caused by pearleaf blister es negundi).3 mite (Phytoptus pyri).4

Fig. 11. Hackberry witches broom caused by Eriophyes Fig. 12. Example of a stem gall mite (Aceria sp.) on celtis.3 maple.8

Fig. 5. Erineum on Rocky Mountain Maple caused by Eri- Fig. 6. Fingergalls on chokecherry caused by Phytoptus ophyes calaceris.5 emarginate.4

Fig. 13. Poplar bud gall caused by Eriophyes parapopuli.3 Fig. 14. Damage caused by rose rosette virus transmitted by Phyllocoptes fructiphilus.4 Photo Credits 1. Texas A&M University, http://cookislands.bishopmuseum.org/species.asp?i 6. Clark, J.C. University of California Statewide IPM Project. d=9294. 7. Solomon, J. USDA Forest Service. Bugwood.org. 8. Csoka, G. Hungary Forest Research Institute. Bugwood.org. 2. Eric Erbe, USDA Agricultural Research Service, Bugwood.org. 3. Whitney Cranshaw, Colorado State University, Bugwood.org. Fig. 7. Bronzing of pear leaves caused by pear rust mite Fig. 8. Russeting of pear fruit by pear rust mite (Epitrimerus 4. Keifer, H.H., Baker, E.W., Kono, T., Delfinado, M., and Styer, W.E. An (Epitrimerus pyri).6 pyri).6 Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites. 5. Ciesla, W.M. Forest Health International. Bugwood.org. requires full coverage of foliage (top and bottom) Control to be effective. Frequent applications are needed, eriophyid mite damage occurs on many plant species but may cause plant stress if used too often (inhibits and often does not impact long term health. Because photosynthesis). Common eriophyid mites affecting plants in Utah of this, chemical pesticides should not be considered a • Sulfur: Sulfur has long been used for mite control. Common Name Scientific Name Host Plants Damage Description primary management option. Full coverage is necessary for control. Do not apply russet mite lycopersici tomato, nightshade plants new infestations turn lower stems and leaves brown, when temperatures exceed 90°F, or during periods of (Solanaceae) eventually withering; rusetting of tomato fruit; death high humidity. Non-Chemical Control • Neem oil: Azadirachtin (group unknown) is a bo- honeylocust rust mite Aculops spp. honeylocust feeding on undersides of leaves causes bronzing that is Cultural control practices that modify the growing envi- tanical insect growth regulator acquired from neem visible by late summer ronment can reduce the occurrence of unwanted pests. trees. peach silver mite Aculus cornutus peach, nectarine, almond silvering of leaves in late summer before leaf drop • Pesticide avoidance: Overuse of insecticides and • Predatory mites: Naturally occurring predatory willow pouchgall mite Aculops tetanothrix willow 2-3 mm diameter irregular and beadlike galls usually miticides can eliminate natural predators, and can mites often feed on Eriophyid mites and can keep located near the leaf midrib or between veins; gall color lead to pest resistance, making long-term control populations at tolerable levels. Avoid the use of is pink to red-purple to yellow and ranges from fuzzy, rough, to smooth; galls may cover whole leaf difficult. broad-spectrum insecticides to preserve predatory mites. Low or extinct populations of predatory mites apple rust mite Aculus schlechtendali apple injured terminal growth; lengthwise leaf curl; fruit ruset- • Monitor/scout: Periodic examination of plant mate- my be supplemented with predatory mites available ting rial reveal Eriophyid populations before they increase for order. One good option for hot arid regions is privet rust mite Asculus ligustri privet scratched appearance on top of leaves turning brown; to damaging numbers. Galendromus occidentalis (western predatory mite). leaf curl on young leaves • Plant selection: Use plants that are less susceptible Other species of predatory mites are available, but grape erineum mite Colomerus vitis grape deformation of bud clusters; felty erineum on lower leaf to eriophyid mites, and that are adapted to Utah’s work best in humid conditions, such as in a green- surface followed by blister-like swellings on upper leaf arid climate; contact your local USU Extension office house. Rocky Mountain Maple Eriophyes calaceris Rocky Mountain Maple greenish yellow to pink, crimson, or purple-red erineum for recommendations. Make sure plants or planting erineum mite on upper leaf surface, usually missing the major veins material you select are free from eriophyid mites. Insecticides and Miticides (Fig. 5) • Prune: Remove infested leaves or branches and hackberry mite Eriophyes celtis hackberry thin, short, stunted, and tightly bunched twigs resulting Table 1 contains an abbreviated list of active ingredients remove from the property. in witches’ brooms (Fig. 11) effective against Eriophyid mites. Make sure the host ash flowergall mite Eriophyes fraxiniflora ash infloresence gall (Fig. 10) • Plant removal: Heavily infested plants such as toma- plant is listed on product label you choose. toes and wheat, may need to be removed to reduce boxelder pouchgall mite Eriophyes negundi boxelder pouch-like galls on upper leaf surface created by inden- • When using pesticides, rotate the chemical group the spread of mites. Some mites have secondary tations on the underside of leaves, filled with fine white on a yearly basis to avoid insect resistance. Chemi- hairs-galls are mostly solitary, located between veins host plants, so removal of host weeds minimizes cal groups are listed in Table 1. sources of re-infestation. cottonwood catkin gall mite Eriophyes newessegi poplar (Populus spp.) grape-like growths/distortions of catkins; affected cat- • For gall-forming mites, once visible damage such as kins remain on tree until mid summer (Fig. 9) galls are observed, it is often too late to treat during poplar budgall mite Eriophyes parapopuli poplar irregular, asymmetrical, bumpy, solid mass of fleshy Chemical Control that growing season. swelling of the bud (Fig. 13) If severe infestations are causing major aesthetic dam- wheat curl mite/bulb mite barley, oats, corn, wheat, Poa leaf curling; red-streaked corn; leaf margin curling; age, tree stress, or crop economic loss, insecticides/miti- spp., Agropyron spp., foxtail brown blistering on bulbs; can transmit wheat streak cides may be necessary. Consider reduced-risk pesticides Active Ingredient Chemical Group barley, onion, , tulip mosiac virus to limit negative impacts on beneficial insects and the abamectin 6 aspen gall mite Phyllocoptes didelphus quacking aspen circular, shallow galls, 5-15 mm in diameter; pouch-like environment. Occasionally, broad-spectrum insecti- bifenthrin 3A galls on upper side of leaf; pockets on undersides of cides/miticides, or those that kill not only your target pest, leaves are filled with yellowish leaf growth carbaryl 1A but many other , may be necessary for quick chokecherry fingergall mite Phytoptus emarginate chokecherry, various plum elongate, finger-like galls scattered over upper surface of reductions in mite numbers. The downside of broad- deltamethrin 3A species (Prunus spp.) leaf; green to yellow turning brown (Fig. 6) spectrum insecticides is that they can eliminate predators imidacloprid 4A alder pouchgall mite Phytoptus laevis alder (Alnus spp.) multi-sized, roundish, green-yellow to reddish-brown and lead to chemical resistance in eriophyid mites and malathion 1B galls located on both sides of leaves other insect populations (if used improperly). permethrin 3A appleleaf blister mite Phytoptus mali apple blister-like galls on upper surface of leaves; yellow- pyrethrin 3A pearleaf blister mite Phytoptus pyri pear green turning brown; brown, blister-like lesions on fruit (Fig. 4) Reduced-Risk Chemicals Table 1. Broad-spectrum insecticides for Eriophyid mite mountain-ash pouchgall mite Phytoptus sorbi mountain-ash blister-like galls on the upper surface of leaves; yellow- • Horticultural soaps and oils: Apply dormant weight control, and their chemical group. Use a different chemi- green turning brown cal group every year to minimize pest resistance.1 horticultural oils 7-10 days before bud break and pine needle eriophyid mite Trisetacus spp. pine (Pinus spp.), Douglas-fir clustering of aborted buds; stunted needles; needle yel- again at bud break. Proper timing targets eriophyid lowing or browning mites and preserves beneficial arthropods. During Precautionary Statement: Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or the summer soaps and summer weight oils offer mite information mentioned in this document. All pesticides are labeled with active ingredients, directions for use, and hazards, and not all are registered for edible crops. “Restricted use” control or suppression. Proper timing can also target pesticides may only be applied by a licensed applicator. The pesticide applicator is legally responsible for proper use. USU makes no endorsement of the products listed herein.

other common plant pests such as aphids. Test for Utah State University is committed to providing an environment free from harassment and other forms of illegal discrimination based on race, color, religion, sex, national origin, age (40 and older), dis- ability, and veteran’s status. USU’s policy also prohibits discrimination on the basis of sexual orientation in employment and academic related practices and decisions. Utah State University employees phytotoxicity before spraying the whole plant. and students cannot, because of race, color, religion, sex, national origin, age, disability, or veteran’s status, refuse to hire; discharge; promote; demote; terminate; discriminate in compensation; or discriminate regarding terms, privileges, or conditions of employment, against any person otherwise qualified. Employees and students also cannot discriminate in the classroom, residence halls, or in • Kaolin clay: A fine clay applied to plants in a liquid on/off campus, USU-sponsored events and activities. This publication is issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Dept. of Ag., Noelle E. Cockett, Vice President for Extension and Agriculture, Utah State University. solution. Kaolin clay acts as a feeding deterrent, and Fact Sheet Series: Insects - Landscape and Ornamental; Tree Fruit; Small Fruit

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